A pointing device such as a joy stick, track ball, and so forth, has since been in use as input means for a personal computer, cellular phone, and so forth. As a sensor of the pointing device, an optical sensor, a pressure sensitive sensor, variable resistance sensor, and magnetic detection sensor have been put to commercial use, however, among those, the magnetic detection sensor small in size, having a long service life, has lately become a favorite one in the market. In particular, a sensor with Hall elements assembled therein has since been in widespread use because it is small in size and simple in construction.
FIG. 13 is a perspective view of a cellular phone disclosed in JP-A 2002-150904, A, for illustrating the construction of a magnetic sensor for use in a conventional pointing device. FIG. 14 is a sectional view of the principal part thereof, taken on line A-A′ in FIG. 13.
In FIG. 14, an input unit 18 which is a part of the pointing device and is made up of a magnetic sensor and a magnet holder, comprises the magnetic sensor made up of four Hall elements, 2a through 2d (Hall elements 2b, 2d are not illustrated), disposed in annular fashion around the center of the input unit 18 on top of a printed circuit board 22, and a magnet holder 23 made of, for example, rubber, wherein a magnet 26 is disposed so as to oppose the Hall elements, 2a through 2d, respectively, with a spacing interposed between the magnet 26 and the respective Hall elements. The magnet holder 23 comprises a key mat 21 annular in shape, disposed on the printed circuit board 22, a bridging part 25 linking the key mat 21 integrally with an input unit body 20 incorporating the magnet 26, and a cylindrical column 24 extended from the center of the underside of the input unit body 20 to the printed circuit board 22.
The input unit body 20 is tilted towards one side when portions thereof, other than the center, are pressed down, whereupon the spacing between the magnet 26 and the respective Hall elements, 2a through 2d, undergoes a change. That is, the Hall elements, 2a through 2d, detect a change in magnetism, accompanying such a change in the respective spacings.
Upon displacement of the magnet 26, the Hall elements, 2a through 2d, detect a magnetic field strength as expressed by the function of a distance between the magnet and each of the Hall elements, 2a through 2d, and an orientation of the magnet, and cause a Hall voltage to occur at right angles to the direction of a current flowing through the Hall elements, 2a through 2d, respectively, and the magnetic field of the magnet FIG. 15 is a circuit diagram broadly showing a magnetic sensor and a circuit for processing a detection output of the magnetic sensor, as disclosed in JP-A H10-20999, A, for explaining a conventional magnetic sensor.
In FIG. 15, outputs of a magnetic sensor 27 comprising respective Hall elements disposed in the x-axis direction and respective Hall elements disposed in the y-axis direction are delivered to a pointing control circuit 28 comprising differential amplifiers 29, an A/D converter 30, a detection controller 31, and an output controller 32 to be thereby processed.
In the pointing control circuit 28, the outputs of the magnetic sensor 27 are amplified by the differential amplifiers 29, respectively, the respective outputs thereof are converted into digital values by the A/D converter 30, and digital outputs thereof are converted into an x-axis coordinate value and a y-axis coordinate value, respectively, by the detection controller 31 to be thereby sent out to the output controller 32.
As is evident from the foregoing explanation, with the conventional pointing device, the magnetic sensor and the pointing control circuit for processing the output of the magnetic sensor have occupied individual disposition regions, respectively, so that in the case of a small-size information equipment, an area dedicated for the pointing control circuit has become too large to be negligible.
Further, with the conventional pointing device, gallium arsenide (GaAs), indium antimonide (InSb), and so forth have been used as material for the Hall elements as constituent members of the magnetic sensor, however, Hall elements using silicon have not been in widespread use. This is because in the case of implementing integration of the Hall elements using silicon, it is difficult to obtain sufficient magnetic sensitivity in comparison with the case of using the material as described above.